Gill nets are nets that use a wide mesh to entangle or trap fish. These nets may be as long as 13,000 meters. The mesh is designed to allow a fish's head to fit through, but not the body. When a fish tries to back out from the meshing its gills will become caught in the net. Often fish will just become entangle in this loose mesh. The meshing of a gill net is tied in between two lines. One line is weighted; this is called the lead line. Another line has buoys attached to it; this is called the float line. The buoyant forces of the float line hold the net upright in the water, while the lead line anchors the net. Gill nets can fish the surface, bottom, or midwater of most types of bodies of water, such as bays, harbors and the open ocean. Some gill nets are anchored to the bottom, but many are free floating. Gill nets are placed in the water by a fishing vessel then retrieved at a later time, most often the next day. Both anchored and free floating gill nets can become lost due to storms, tides, currents, poor attachment of anchors or floats, or entanglement with other vessels or fishing gear. When these nets become broken or lost they continue to serve as effective traps. Lost nets or pieces of nets are called “ghost nets” these nets can continue to kill fish, turtles, birds, and marine mammals for several years.